Patent GB-739595-A (GB)
Title: Facsimile receiving apparatus
IPC: H04N1/38
Filed: 1952-12-05
Abstract: 739,595. Copying-telegraphy receivers. CREED & CO., Ltd. Dec. 5, 1952 [Dec. 13, 1951], No. 30917/52. Class 40 (3). Apparatus for phasing a facsimile receiver scanning mechanism with an associated transmitter from which a train of phasing impulses is received, comprises means to generate a train of local phasing impulses individually produced in a predetermined position of the scanning mechanism, control means to render the frequency of the local phasing impulses different by a given amount from the frequency of the received phasing impulses, phasing means for comparing the times of occurrence of the received and local phasing impulses, and means responsive to the coincidence of the received and local phasing impulses to render ineffective the control means. In the absence of the stand-by or the end of message signal of 12.5 kc/s. the valve 99 conducts and relay EMD is energized. When this signal is received by the signal receiving circuit of Fig. 2 via valves 51, 53, 96 and the tuned circuit 98, valve 99 is cut-off so that relay EMD releases. To prevent the 12.5 kc/s. signal from being applied to the recording stylus, relay EMD in its released condition applies ground to the facsimile signal circuit. The phasing signal comprising a 25 kc/s. carrier modulated by a 30-cycle rectangular wave appears at the grid of the valve 120, Fig. 3, as a train of positive rectangular pulses. The positive pulses at the cathode of the valve 120 applied in succession via a capacitor 127 and leak resistor 128 are effective to cut off the normally conducting valve 126 so that a phasing signal detector relay PHD is de-energized. The negative pulses at the anode of valve 120 cut-off valve 135 which applies corresponding positive pulses to a grid of the valve 141. Negative impulses applied to a coil 35 by a magnetic member on the shaft of the stylus motor 20 are applied to the grid of a valve 138, and the positive impulses from the anode are also applied to the same grid of the valve 141 which conducts solely when the positive pulses applied are in coincidence. An auxiliary motor, Fig. 2 (not shown) increases the speed of the motor 20 from 1800 to 1830 r.p.m. and when coincidence is established between the pulses from the coil 35 and the phasing pulses, a phasing relay PH operates and disconnects the auxiliary motor. In the inoperative condition of the apparatus solely the phasing-signal detector relay PHD is energized, but following the transmission of the standby signal constituted by a short signal of frequency 12.5 kc/s., a relay EMD is operated and applies power from A.C. source over contacts of a relay ST to a stylus-belt motor 20. Power is also applied via a delay network comprising resistor 233 and capacitor 234 to the starter anode circuit of a glow-discharge tube 230. When the tube 230 conducts relay ST operates and transfers the motor 20 to the output of a synchronous power amplifier. The operation of relay EMD applies power over released contacts of a " run " relay RR and of a phasing relay PH to an auxiliary rotary transformer drive motor, Fig. 4 (not shown), which is arranged to increase the frequency of the input of the synchronous power amplifier to 61 cycles so that the motor 20 runs at 1830 r.p.m. instead of 1800 r.p.m. whilst the auxiliary motor is operative. When the phasing signal is received a negative bias is developed at the input to a phasing-signal detector tube 126 so that its reduced anode current allows relay PHD to release, thereby switching in a timer circuit 237 which measures a desired phasing period during which the receiver, running at a slightly different rate from that of the transmitter, will come into phase so that the impulse applied from the generator on the shaft of the motor 20 and the received synchronizing impulse derived from valves 120, 135, 138 will, when applied simultaneously to the grid of the thyratron 141, cause it to conduct and operate relay PH which disconnects the auxiliary motor. General operation. The circuits, Figs. 6, 7, and operating elements are generally similar to those described in Figs. 42, 43 of Specification 734,435. At the end of the phasing period, switch 239 of timer 237 operates, energizing relay RR which applies power to normal feed motor 251 and platen advance motor 250, steps up the power supply of the signal-recording amplifier and operates a fast-feed relay FF. The end-of-message signal momentarily releases relay EMD, which alloys relay RR to fall off and operate fast-feed motor 278. The further operation is determined by a switch 266 which determines whether a fixed length of blank is to be fed out before the paper-severing action takes place, or whether a fixed total length of blank is to be provided. A cam operates a meter switch 261 releasing relay FF which stops the fast-feed motor and applies power to a knife-relay KNF and knife motor 290. When the operation of the knife has been completed, a switch 285 is opened releasing relay KNF and stopping the knife motor. Release of relay RR breaks the direct current supply to relay PH cutting off the thyratron 141 which is now ready to phase the next transmission. Relay ST is slow to release so that the circuit is in readiness for the next transmission which normally follows after a short transmission of the standby signal. If a further transmission is not to take place the standby signal is prolonged and the relay ST releases. The arrangements include the motor stabilizer circuit arrangement described in Specification 717,726, [Group XL (c)]. Specification 739,594 also is referred to.